Cobalt pentammine separation



Felix A. Schaufelberger, Yonkers, and Alfred M. Czikk,

Flushing, N. Y., assignors to Chemical Construction Corporation, NewYork, N. Y., a corporation of Delaware No Drawing. Application December23, 1953, Serial No. 400,115

4 Claims. (Cl. 23-117) This invention relates to hydrometallurgy ofcobalt and nickel. More particularly it is concerned with the separationof these metals one from the other when both are contained in the sameliquor. Still more particularly, it involves a new method of obtaining asubstantially nickelfree cobalt solution from liquors containing themixed soluble salts of both metals.

Nickel and cobalt metals and their naturally-occurring minerals are verysimilar to one another in both physical and chemical properties.Moreover both metals generally occur together in their natural depositsand cannot be separated by conventional ore dressing methods. For thesereasons, both metals are generally present, in varying amounts, insolutions that result from any type of leaching of either nickel orcobalt natural or intermediate products.

In conventional metallurgy of either nickel or cobalt, the presence ofrelatively large quantities of the minor metal in the ores andconcentrates of the major one has always been a serious and difiicultproblem. When small amounts of cobalt are present in nickelconcentrates, most of that cobalt is discarded in the slag from nickelsmelting. The remainder is sold in the nickel bullion or cathodes asnickel metal. Very little is recovered and sold as cobalt metalprimarily because the cost of separation by present methods is at least'as great as the additional value of the cobalt metal.

When small arnounts of nickel are present in cobalt concentrates andtherefore in the cobalt solutions this nickel is generally eitherdiscarded at considerable loss or is recovered with the cobalt. In thelatter case, the nickel becomes an impuri y in the cobalt metal, and theproducer is generally not paid for it. In some cases, certain nickel andcobalt mixed metals are marketable as such, but usually at a price belowthe value of the pure metals in separate products.

It is apparent therefore that a process for the efiicient separation ofcobalt and nickel into separate products would be very useful in bothnickel and cobalt metallurgy.

Many processes have been either proposed or used for the treatment ofliquors containing dissolved cobalt and nickel salts. Most of theseinvolve the oxidation of cobalt to cobaltic hydroxide, while the liquoris being partimly neutralized with an alkali. Cobalt is easier tooxidize, and the resulting cobaltic salt will hydrolyze and precipitatefrom a slightly more acidic solution than will the parallel nickelhydroxide.

There have been also suggested several methods of separating nickel andcobalt from ammonium carbonate leach liquors. Most of these involvefractional distillation of the ammonium carbonate. The mother liquor, atdifferent stages in the process, thereby becomes concentrated witheither nickel or cobalt. This liquor may then be removed and treatedseparately. The residue may be redissolved and retreated separately.

The above types of processes for the production of nickel or cobaltresult in products containing relatively large amounts of the othermetal. This relatively poor States Patent 2,767,054 Patented Oct. 16,1956 separation is probably due to the fact that the separations aremade by precipitation of hydroxide or basic carbonate solids. Thesesolids always occlude or absorb large quantitim of the solution fromwhich they are precipitated.

More recently there have been several new separation proceduressuggested. One such procedure comprises recovering cobalt as cobaltichexammine sulfate. The procedure comprises adjusting the solids contentof the liquor to provide at least suflicient ammonia to form cobalthexammine and at least sutiicient anions to satisfy the cobalt in itstrivalent state. The adjusted solution is then oxidized and heated toabout 250 F. to precipitate a yellow-orange crystalline cobaltic amminesalt, substan tially free of nickel. This procedure provides for anexcellent separation and produces a high purity cobalt productparticularly when treating liquors having low cobalt to nickel ratios.It, however, is not particularly satisfactory for liquors having highcobalt to nickel ratios since it involves separating the major metalconstituent in solid form. In addition it requires high ammoniaconcentrations to insure formation of the hexammine as well as hightemperatures and pressures.

Another recently suggested process for effecting a nickel-cobaltseparation comprises high temperature reduction with hydrogen in whichnickel in the form of nickel ammine complexes is preferentially reducedwith respect to cobalt. This may then be followed by reduction of thecobalt. While products of excellent purity are also obtained in thismethod it also has the disadvantages that it requires high temperaturesand pressures and is preferably applied to liquors having high nickel tocobalt ratios.

Still another of these new procedures comprises treatting a nickelcobalt liquor at room temperature with carbon dioxide whereby cobaltcarbonate is precipitated. This provides cobalt products of satisfactorypurity particularly from liquors having high cobalt to nickel ratios.Cobalt carbonate moreover is easily calcined and reduced to obtain ametal product. However, the problem created by the handling of largevolumes of carbon dioxide is a disadvantage.

In copending application Serial No. 400,112 of F. A. Schaufelberger, oneof the inventors herein, filed of even date, there is disclosed a veryeifective method for separating cobalt from nickel. In general itcomprises adjusting the ammonia and ammonium sulfate contents of anickel and cobalt salt liquor and subjecting adjusted liquor tooxidation with a sulfur-free, oxygen-bearing oxidizing gas. The ammoniacontent of the liquor is adjusted so as to form a complex ammine salt ofthe dissolved cobalt content which, when the cobalt is in its trivalentstate, is stable and soluble under acid conditions. Thus, sufficientammonia is added, if necessary, to provide about 5 mols of ammonia foreach tool of dissolved cobalt plus about 5 mols of ammonia for each molof dissolved nickel. After oxidation, the hydrogen ion concentration isadjusted to at least that equivalent to a pH of 4 as by the addition ofsulfuric acid. This adjustment, however, is not conducted beyond ahydrogen ion concentration equivalent to a 2% sulfuric acid solution.Within this range of hydrogen ion concentrations cobaltic pentammine isquite stable and very soluble. In contrast the nickel pentammine isdecidedly unstable and insoluble and precipitates as the nickel ammoniumdouble salt.

By the procedure of the above identified copending application, asubstantially pure cobalt solution is obtained. Except under excessiveconcentrations of ammonium sulfate, however, it is impossible,regardless of the original concentration of nickel in solution, toreduce the dissolved nickel content below about one gram per liter.Accordingly, it may be necessary, particularly where the cobalt tonickel ratio is low, to adjust the ammonium sulfate concentration tofurther decrease the solubility of nickel ammonium sulfate, thereby,effecting a greater nickel from cobalt separation. This adjustment maybe made at any of severalstages in the'process. Regardless of wheremade, it is possible to reduce the nickel solubility to as little asabout 0.2 gram per liter by increasing the ammonium sulfateconcentration to about 4.5 mole or more per liter. 7

While nickel solubility can be greatly reduced in this manner, ammoniumsulfate concentration in the residual cobalt liquor is greatlyincreased. While this generally would be of no particular concern exceptfor recovery of the ammonium sulfate, high ammonium sulfateconcentrations are influential in certain procedures for treating cobaltliquors to recover therefrom the cobalt content as metal. This isparticularly true when the procedure comprises gas reduction withhydrogen. A high ammonium sulfate content in such a procedure greatlyreduces the recovery of cobalt metal powder. It is, therefore, theprimary object of this invention to provide a method of further reducingnickel ammonium sulfate solubility in an oxidized liquor as describedabove without, however, influencing the effectiveness of subsequenttreatment for recovery of cobalt from the residual cobalt liquor.

This object has been met by an improvement which is surprisinglyeffective, but which does not upset the simplicity and/ or economy ofthe over-all process. In gencern, however, this procedure is notparticularly desirable because it requires the presence of an excessiveamount of cobaltous ions to insure reduction of nickel content to thedesired extent. This, in turn, greatly reduces the recovery of cobalt insolution.

Alternatively, cobaltous ion concentration may be adjusted afteroxidation by the addition of acobaltous compound. This may, for example,comprise addition of residual cobalt solution resulting from treatmentof nickel precipitate. Cobalt may also be added as various compoundsother than the sulfate provided they ionize. While the addition ofanions other than the sulfate does not appear to adversely influence theseparation of the instant process, provided sufiicient sulfate ions areotherwise rnade available their presence may seriously affect subsequenttreatment of the residual cobalt solution. Accordingly, while notnecessary, it is definitely preferable when increasing the cobaltouscontent by the addition of 'eral, this novel method of reducing nickelsolubility may i be quite simply stated. It comprises appropriatelycontrolling the cobaltous ion concentration of the oxidized liquor so asto precipitate a cobalt nickel ammonium triple salt. This improvementquite remarkably eliminates the disadvantages associated with the use ofammonium sulfate. At the same time the presence of cobaltous sulfatereduces nickel solubility to an extent which would require some 10 totimes as much ammonium sulfate. substantially zero. invention is quitesimple, there are, nevertheless, certain conditions whichmustbe'observed to obtain optimum results.

The lowering of nickel solubility effected by the presence of cobaltousions is due to the unexpected finding that under the particularconditions of precipitation cobalt-nickel-ammonium triple salt issubstantially less soluble than nickel ammonium double salt. The greaterthe Moreover, nickel solubility may be reduced to While the generalstatement of the.

amount of cobaltous cobalt in solution, moreover, the

lower may the dissolved nickel content be taken since the solubility ofthe triple salt has been found to decrease as the cobalt to nickel ratiothereof increases. Thus the amount of cobaltous ions in solution may bequite widely varied.

This amount is most easily described in relation to the cobalt to nickelmol ratio of the precipitated salt. At lower ratios, i-. e., 1:1 to1.52:1, the residual content of nickel cannot be reduced to as low asmay sometimes be desirable. At ratios of about 3:1, the dissolved nickelcontent can be reduced to as little as 0.1 gram per liter. On the otherhand, the solubility of triple salts having cobalt to nickel ratios ofabout 3.5 :l and higher is not sufficiently less to warrantprecipitation thereof. Moreover, subsequent treatment of nickel productshaving such high cobalt contents as for instance by preferentialreduction with hydrogen, creates a recycle problem with respect to theresidual cobalt solution. While the cobalt to nickel ratio of theprecipitated salt may, therefore, be varied, optimum results areobtained when the nickel to cobalt ratio is from about 2.5-3.5 :1 andpreferably 3:1.

The presence of the desired concentration of cobaltous ions intheoxidized solution may be provided for in various ways; For instance, itmay be accomplished by conducting oxidation of the original liquor so asto incompletely oxidize initially present cobaltous cobalt. Since it isthe last gram/liter of nickel in solution that is of cona cobaltcompound to restrict the anion to sulfate.

increase of the cobaltous content by addition of a cobaltous compoundmay be done at various stages in the process after oxidation. However,if done before any nickel precipitation, the amount of cobaltouscompound required will be excessive. This is subject to disadvantagessimilar to those described above in the discussion of incomplete cobaltoxidation. Since it is nickel solubilities of about one gram/liter, andless, which are of concern, it is preferable to, precipitate nickeltothe optimum extent under conditions arising from the initial ammonia andammonium sulfate adjustment as described in the above noted copendingapplication. The cobaltous ion concentration may then be suitablyadjusted to reduce nickel solubility to the desired extent. In this waynot only are the disadvantages of excessive cobaltous ion concentrationavoided, but two nickel products may be taken, the first of which issubstantially cobalt-free nickel ammonium sulfate. 7 V

The process of this invention may also be conveniently combined withreduction of nickel solubility by increasing the ammonium sulfateconcentration. By proper adjustment of the two, it is possible to reducenickel solubility as effectively as with either alone. At the same time,ammonium sulfate content of the residual solution and the Co/ Ni ratioof the nickel precipitate are lower than could be obtained by adjustingseparately the ammonium sulfate and cobaltous ion concentrationsrespectively. I I

Attention is directed to copending applications, Serial Nos. 400,113 and400,114, filed of even date by the same applicants. These applicationsshow methods of improving the separation of the process of above notedapplication, Serial No. 400,112, which comprise'boiling and steamstripping, respectively, of the oxidized solution. The process of thisinvention may be conveniently combined with either or both of thesemethods.

The following example will further illustrate the invention EXAMPLEparts and cobaltous content adjusted by adding cobalt ammonium sulfatein amounts of 0 'gm./l., 6.2 gm./l., 9.2

gm./l., and 12.3 gm./l. Results obtained after crystallization areindicated in thetable. 1

Table FILTRATE RESIDUE Sample Added CO(NH4)2SO4 Co Ni Co Ni (s-I (av/(s-I I i (p (p (JO/M cent) cent) We claim:

1. In a hydrometallurgical process for recovering a substantiallynickel-free cobalt solution from a liquor containing dissolved nickeland cobalt which comprises adjusting the solutes content of said liquorto provide about 5 mols of ammonia for each mol of dissolved cobalt plusabout 5 mols of ammonia for each mol of dissolved nickel and a sulfateion concentration at least sufiicient to satisfy the dissolved cobaltcontent in its trivalent state and dissolved nickel in its bivalentstate; oxidizing the adjusted liquor with a sulfur-free, oxygenbearingoxidizing gas; introducing sulfuric acid into said oxidized liquor toproduce a hydrogen ion concentration at least equivalent to a pH ofabout 4, whereby a substantially cobalt-free, nickel-bearing precipitateis formed; and separating said precipitate, leaving a solutioncontaining cobalt as acid soluble, acid stable cobaltic ammine sulfateand a minor amount of nickel in its bivalent state, there beinginsuflicient dissolved bivalent cobalt to form a cobaltous-bearingprecipitate, the improved method adapted to decrease the nickel contentof said solution which comprises: increasing the cobaltous ion contentof said solution sufficient to provide a cobaltous 6 ion to nickelousion ratio of at least about 1:1 whereby cobaltous-nickelous-ammoniumsulfate is precipitated, and separating said precipitate.

2. A method according to claim 1 in which the inincrease in cobaltousion content is sufiicient to provide a cobaltous ion to nickelous ionratio of about 2.5-3.5: 1.

3. A method according to claim 1 in which the increase in cobaltous ioncontent is sufficient to decrease the dissolved nickel content to lessthan 1.0 gram per liter, said decrease being conducted withoutsubstantially increasing the ammonium sulfate concentration of saidsolution.

4. A method according to claim 1 in which the cobaltous content isincreased by adding a cobaltous compound.

References Cited in the file of this patent UNITED STATES PATENTS2,531,336 Hills et a1 Nov. 21, 1950 2,576,314 Forward Nov. 27, 19512,588,265 McGauley Mar. 4, 1952 2,647,820 Forward Aug. 4, 1953 2,647,827McGauley Aug. 4, 1953 2,647,828 McGauley Aug. 4, 1953 OTHER REFERENCESMellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry,vol. 14, 1935, published by Longmans, Green and Co., New York, pages440, 441 and 444.

Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry,vol. 15, 1936, pages 477 and 478.

Vohl: article on Ann. Chem. Justus Liebigs 94, pages 57 to 79, inclusive(1855).

1. IN A HYDROMETALLURGICAL PROCESS FOR RECOVERING A SUBSTANTIALLYNICKEL-FREE COBALT SOLUTION FROM A LIQUOR CONTAINING DISSOLVED NICKELAND COBALT WHICH COMPRISES ADJUSTING THE SOLUTES CONTENT OF SAID LIQUORTO PROVIDE ABOUT 5 MOLS OF AMMONIA FOR EACH MOL OF DISSOLVED COBALT PLUSABOUT 5 MOLS OF AMMONIA FOR EACH MOL OF DISSOLVED NICKEL A SULFATE IONCONCENTRATION AT LEAST SUFFICIENT TO SATISFY THE DISSOLVED COBALTCONTENT IN ITS TRIVALENT STATE AND DISSOLVED NICKEL IN ITS BIVALENTSTATE; OXIDIZING THE ADJUSTED LIQUOR WITH A SULFURIC ACID INTO SAIDBEARING OXIDIZING GAS; INTRODUCING SULFURIC ACID INTO SAID OXIDIZEDLIQUOR TO PRODUCE A HYDROGEN ION CONCENTRATION AT LEAST EQUIVALENT TO APH OF ABOUT 4, WHEREBY A SUBSTANTIALLYH COBALT-FREE, NICKEL-BEARINGPRECIPITATE IS FORMED; AND SEPARATING SAID PRECIPITATE, LEAVING ASOLUTION CONTAINING COBALT AS ACID SOLUBLE, ACID STABLE COBALTIC AMMINESULFATE AND A MINOR AMOUNT OF NICKEL IN ITS BIVALENT STATE, THERE BEINGINSUFFICIENT DISSOLVED BIVALENT COBALT TO FORM A COBALTOUS-BEARINGPRECIPITATE, THE IMPROVED METHOD ADAPTED TO DECREASE THE NICKEL CONTENTOF SAID SOLUTION WHICH COMPRISES: INCREASING THE COBALTOUS ION CONTENTOF SAID SOLUTION SUFFICIENT TO PROVIDE A COBALTOUS ION TO NICKELOUS IONRATION OF AT LEAST ABOUT 1:1 WHEREBY COBALTOUS-NICKELOUS-AMMONIUMSULFATE IS PRECIPITATED, AND SEPARATING SAID PRECIPITATE.